Packaged galvanic anodes



April 29, 1969 P. F. GEORGE 3,441,491

PACKAGED GALVANC ANODES Filed March 5, 1966 Xwlww INVENTOR. Percy F. George MFM@ United States Patent Op 3,441,491 PACKAGED GALVANIC ANODES Percy F. George, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Filed Mar. 3, 1966, Ser. No. 531,395 Int. Cl. C23f 13/ 00 U.S. Cl. 204-197 6 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a packaged galvanic anode useful in cathodic protection systems. The packaged galvanic anode includes a relatively low potential high efficiency galvanic anode containing a central ferrous core, a relatively high potential low efiiciency galvanic anode having a substantially greater length than width attached at one end to the ferrous metal core but separated from and encircling at least a portion of the low potential anode. This anode combination is contained Within a water-permeable bag containing a backll composition of a watersoluble magnesium salt, such as magnesium chloride, in combination with bentonite and alternatively also containing sulfates such as calcium and sodium sulfate.

This invention relates to a new and improved packaged galvanic anode and more particularly relates to a packaged galvanic anode suitable for use in either sea water or earth environments.

It is known that the tendency of steel or similar materials to undergo serious corrosion can be offset by cathodic protection. Two of the important areas for cathodic protection are the protection of structures such as ships or piers which are in contact with sea water and the protection of structures such as pipelines in contact with soil. With protection of metal structures in Contact with these environments presents slightly different problems, basically a sacrificial anode is employed which is electronegative relative to the structure to be protected. Electrical connection between such anode and the structure to `be protected causes a current to fiow which maintains the metal structure cathodic and therefore minimizes or eliminates corrosion. The sacrificial anodes employed are usually made predominantly of magnesium, zinc or aluminum and may be suspended directly in the sea water, or buried in the ground adjacent to the structure to be protected or such anodes may be surrounded by a prepared bed or backll designed to control the chemical nature of the anode environment. All such anodes are plagued by one continuing problem, i.e. anode materials can have either high solution potential (volts) or high anode efficiency (amp. hrs/lb.) but seldom does one material have both. For example, if the anode is made solely from material giving a high solution potential, the anode is depleted at an unnecessarily high rate. On the other hand, if the anode employed has high anode efficiency and low solution potential months or even years may be required to polarize the structure, i.e. bring the structure to a protective potential.

It is an object of this invention, therefore, to provide an anode which will provide sufficient initial voltage to provide rapid initial protection and in which voltage decreases in time to provide long term cathodic protection. A further object is to provide such an anode in packaged form suitable for use in both sea water and soil environments. A further object is to provide a packaged anode combined with a backfill to achieve optimum solution potential and efficiency. These and other objects and advantages will become obvious from a reading of the following detailed specification in conjunction with the appended drawing.

3 ,441,491 Patented Apr. 29, 1969 The figure of the drawing shows a longitudinal cross section of one embodiment of the packaged galvanic anode of the present invention.

It has now been discovered in accordance with the present invention that an improved cathodic protection system having both an initial high solution potential and a long useful anode life, i.e. high efficiency, is provided by the combination of a relatively low solution potential, high efficiency galvanic anode having a steel core and surrounded by a coil of relatively high potential lower anode efficiency galvanic anode in the form of a strand or wire which is attached at one end to the steel core. Particular advantage is achieved where the present novel combination of anodes is contained within a porous sack containing a backfill of particular composition to provide almost an instant maximum solution potential.

Relatively low solution potential galvanic anodes, as understood by one skilled in the art are those anodes which develop from about 0.9 to about 1.5 volts compared to a standard Cu-CuSO.,t reference electrode. As is known in the art, anodes having such relatively low potentials are commonly made from magnesium alloyed with minor amounts of other meals to lower its potential. Such anodes are likewise made from zinc, or aluminum which may contain small amounts of other metals to modify their electrical or structural properties. Such low potential, high efficiency anodes are usually cylindrical although other shapes can be used. These anodes contain a core of ferrous metal, preferably centered therein, which may be solid or hollow and may extend the full length of the anode or may extend only partly into such anode.

Relatively high solution potential anodes are those which develop a voltage from about 1.55 to about 1.70 volts compared to a standard Cu-CuSO, reference electrode. Typical examples of such relatively high potential low efficiency anode material are relatively pure magnesium and lithium.

In the present invention, the high solution potential low efficiency anode component encircles the low potential high efficiency anode and is in the Iform of a strip, fiber, filament, wire, or the like having a relatively much greater length than width or diameter and formed into a circular or spiral configuration to provide a relatively high surface area. A quantity of such material in strip or other suitable form is used to encircle the relatively low potential anode in a circular or spiral configuration so as not to make contact with the relatively low potential anode. One end of the high potential anode is physically and electrically connected to the ferrous core of the low potential anode by welding or by other suitable means such as mechanical or frictional bonding. Such area of connection between the relatively high potential anode and the ferrous core of the relatively high potential anode and the ferrous core of the relatively low potential anode is electrically insulated from the body of the relatively low potential electrode with an insulating, water-resistant material such as tar, wax, asphaltic material, synthetic resins, and the like.

For optimum in performance, this dual anode structure is ordinarily surrounded by a backfill containing a water-soluble magnesium salt such as magnesium chloride, magnesium bromide, magnesium acetate and the like. A particularly effective `backll composition for sea water use contains a water-soluble magnesium salt in combination with a bentonite clay. In such mixture, it is desirable to have the soluble magnesium salt such as MgCl2 present in an arnout of from about 50 to about 95 weight percent, preferably about 70-80 weight percent with the remainder being bentonite clay. -For use in soil, a particularly effective -backll advantageously contains calicum sulfate and sodium sulfate in addition to the water-soluble magnesium salt and bentonite. In such backll composition it is desirable to have from about 25 to about 75 weight percent soluble magnesium salt, from about to about 50 weight percent CaSO4-2H2O, from about l to about 10 weight percent Na2SO4 and from about l0 to about 30 weight percent bentonite. A backtill of such composition combination with the dual anode structure hereinbefore described provides the environment that produces the maximum instant solution potential of the outside anode.

To provide a packaged anode useful in either sea Water or earth applications, the combination of a relatively high potential anode, relatively low potential high efficiency anode and surrounding backll are contained within a water permeable bag. Preferably the dual anode is substantially centered within such Ibag with the remaining space being substantially llilled with backll composition.

The galvanic anodes and backfill materials are electrically connected to the structure to be protected by means of an insulated lead conneced at one end to the ferrous metal core of the low potential anode and at the other end to the structure. Suitable structures to be protected by means of the galvanic anode strutcure of this invention include iron or steel pipelines immersed in sea water or fresh water or buried in the earth and the like.

The figure shows one embodiment of the anode of the present invention. This assembly comprises, in general, a relatively low potential anode 10, containing a central ferrous metal core 11, and surrounded by a spiral of relatively high potential anode wire 12. An insulated lead wire 17 is attached to the upper end of the ferrous metal core 11 and connects such core with the structure to be protected (not shown). The upper end of the relatively high potential anode wire 12 is attached to the ferrous metal core 11, usually by a spot weld 13 and insulated from the relatively low potential anode 10 by an electrically insulating, water-resistant tar seal 14. The spiral of relatively high potential anode wire 12 is spaced apart from the relatively low potential anode 10 and makes no contact therewith. Such anode assembly ordinarily is enclosed in a backll composition 15 retained by a water permeable bag 16 closed at the upper end around the insulated lead wire 17 by closure means 18.

The following example will more fully illustrate the invention but is not to -be construed as limiting to the scope thereof.

Example l A standard zinc anode 1 inch in diameter, 4 inches long, weighing 407 grams and having a steel bolt as a core was placed in the center of a cloth bag. Around the zinc anode was placed eight turns of 0.125 inch relatively pure magnesium wire weighing 14 grams. The bag was filled with 450 grams of backll containing 75 weight percent magnesium chloride and weight percent bentonite clay. The bag containing such anode was placed below the liquid level in a 55 gallon drum containing about gallons of synthetic sea water and the anode was electrically connected to the steel drum by an insulated lead in wire. Both the lead in wire and one end of the magnesium wire anode were connected to the steel bolt core of the zin-c anode. A coating of tar was applied over such connections to insulate them from contact with the body of zinc anode. The following results were obtained with this anode.

Current from anode Time in minutes to drum (amparos) For comparison, a standard commercial zinc anode l inch in diameter, 4 inches long and weighing 407 grams and having a steel bolt as a core was placed in the center of a cloth bag and the bag was filled with a backfill containing 75 weight percent magnesium chloride and 25 weight percent bentonite clay. The `bag containing such anode lwas placed in the center of a steel 55 gallon drum containing about 30 gallons of synthetic sea Water. The anode was immersed in the saltwater and electrically connected to the steel drum by an insulated lead wire attached at one end to the drum and at the other end to the steel core. Both points of attachment were insulated with a coat of tar. The following results were obtained.

Current from anode to drum (amparos) Time in minutes This comparison clearly shows that the accepted protection level of 0.85 volt was achieved by the anode of this invention after about 7 minutes while the standard commercial anode had not reached the protection potential of 0.85 volt even after 31 minutes.

In a manner similar to the foregoing, aluminum anodes containing central ferrous cores and having solution potentials of between about 0.9 to about 1.5 volt are surrounded by a magnesium lwire which is attached to the ferrous core but separated from the aluminum anode. The dual anode thus prepared is placed in a water-permeable bag and the remaining space in the bag is lled with a backll composition containing from about l0 to about 50 weight percent calcium sulfate, from about 25 to about 75 weight percent magnesium chloride, from about 1 to about 10 weight percent sodium sulfate and from about 10 to about 30 weight percent bentonite clay. The packaged anode is buried in the soil near an iron pipeline section and electrically connected thereto by means of an insulated lead wire between such pipeline section and the steel core of the aluminum anode. Immediate high solution potential is achieved, the pipeline section is rapidly polarized and long term eicient cathodic protection is provided.

Substantially the same results are achieved when the re1- atively high potential, low eiciency anode is a strand of lithium. Likewise, substantially the same results are achieved when the relatively low potential, high eiciency anode is composed of an alloy of magnesium having a potential between about 0.9 and 1.5 volt.

Various modifications can be made in the present invention without departing rfrom the spirit or scope thereof for it is understood that lI limit myself only as defined in the appended claims.

I claim:

1. An improved packaged galvanic anode useful in cathodic protection systems which comprises, in combination a relatively low potential high etliciency galvanic anode containing a central ferrous metal core, a relatively high potential low eiciency galvanic anode having a substantially greater length than width attached at one end to the ferrous metal core but separated from said low potential anode and encircling at least a portion of said low potential anode, a water-permeable bag surrounding said anodes, a backill composition comprising from about 50 to about weight percent of magnesium chloride and from about 5 to about 50 weight percent bentonite.

2. An improved packaged galvanic anode useful in cathodic protection systems which comprises, in combination, a relatively low potential high eiciency galvanic anode containing a central ferrous metal core, a relatively high potential low eiciency galvanic anode having a substantially greater length than width attached at one end to the ferrous metal core but separated from said low potential anode and encircling at least a portion of said low potential anode, a Water-permeable bag surrounding said anodes, and a backll composition consisting essentially of from about 25 to about 75 weight percent of a soluble magnesium salt, from about l to about 50 Weight percent of calcium sulfate, from about 1 to about 10 weight percent of bentonite.

3. The packaged galvanic anode of claim 2 wherein the water-soluble magnesium salt is magnesium chloride.

4. In combination, an iron or steel structure immersed in sea Water or buried in the earth, an improved protective system located near said structure and electrically connected thereto which comprises, in combination, a waterpermeable bag, a relatively low potential high efficiency galvanic anode containing a central ferrous metal core substantially centered in said bag, a relatively high potential low eciency galvanic anode having a substantially greater length than Width attached at one end to said steel core but separated from said low potential anode and encircling at least a portion of said low potential anode, and a backtill composition comprising from about 50 to about 95 weight percent of magnesium chloride and from about 5 to about 50 Weight percent bentonite.

5. In combination, an iron or steel structure immersed in sea Water or buried in the earth, an improved protective system located near said structure and electrically connected thereto which comprises, in combination, a water permeable bag, a relatively low potential high eflicie'ncy galvanic anode containing a central ferrous metal core substantially centered in said bag, a relatively high potential low efriciency galvanic anode having a substantially greater length than width attached at one end to the ferrous metal core but separated from said low potential anode, and a backtill composition consisting essentially of rfrom about 25 to about 75 weight percent of a soluble magnesium salt and from 10 to about 50 weight percent calcium sulfate, from about 1 to about 10 weight percent sodium sulfate and from about 10 to about 30 IWeight percent bentonite. e'

6. The protective system of claim 5 wherein the watersoluble magnesium salt is magnesium chloride.

References Cited UNITED STATES PATENTS 2,478,478 8/ 1949 Grebe 204-197 2,527,361 10/1950 Hunter 204-197 2,565,544 8/l951 Brown 204-148 2,601,214 6/1952 Robinson 204-197 2,765,273 10/ 1956 Lobos 204-197 2,772,231 1l/1956 Waite et al 204-197 FOREIGN PATENTS 489,985 1/1953 Canada.

OTHER REFERENCES Reprint from GAS, April 1952, Magnesium Ribbon Anode, H. A. Robinson, The Dow Chemical Co., p.6.

HOWARD S. WILLIAMS, Primary Examiner.

T. TUNG, Assistant Examiner.

U.S. C1. X.R. 

